Best? Neither, but in a roadside emergency (or just a breakdown) both will respond quickly to your call. Both will try to dispatch a local independent contractor, and both will call emergency first responders for a "Emergency".
But both have countless complaints, either because they couldn't find a contractor close to your location, or because the contractor was incompetent in dealing with RVs. Personally, I had a problem with Coachnet unable to send someone out, they tried to give technical assistance over the phone, but all that amounted to was reading the directions to me (I had the direction book in my hand, and I can read). AAA clearly states in the contract that many locations do not offer RV (especially big RV) service and you will be on your own, you can "try" to get reimbursement is approved. Currently I have Good Sam. I have no complaint, but clearly others do.
Pick one, hope you never use it, and enjoy
Happy Trails.